The 12 Worst Insect Invaders

Stink bugs, bedbugs, emerald ash borers—they're some of the most vile insect invaders around, killing trees and gardens and generally making our lives miserable. We bring you the 12 worst, and let you know where they came from and what they can do.

Locusts

Locusts

They're the original insect plague. Humans have been battling these ravenous winged grasshoppers for millennia.

"All locusts are grasshoppers, but not all grasshoppers are locusts," Greg Sword, an entomologist at Texas A&M University, says. The behavior that separates locusts from their grasshopper brethren is swarming. A single locust isn't worrisome, and locusts like to live alone for most of their lives. But when a group of locusts swarm, they can devastate the vegetation of an entire region, devouring everything in sight. They only start to swarm when the locust population increases to the point that individual locusts are crowded together, triggering a dramatic change in behavior and coloring. Mature locusts begin flying along with the wind, eating as much as their weight (2 grams) in vegetation every day. In areas of Africa where subsistence farming is practiced, large plagues of locusts can devastate the food supply of a region. "They can potentially affect the livelihoods of one out of 10 people on the planet," Sword says.

Australia suffered a massive swarm of Australian plague locusts last year. This year, locusts are making an appearance in China and Central Asia. Here in North America, however, much of the locust threat subsided when the Rocky Mountain locusts went extinct in the early 1900s. "There used to be epic, sky-darkening outbreaks," Sword says. But the huge populations of locusts were probably destroyed by pioneers building towns along the riverbanks where locusts laid their eggs.

Mormon Cricket

Mormon Cricket

Today, the bane of North American farmers in the West is not the locust, but the Mormon cricket. These pests are a huge problem in the southwestern United States, where they not only eat massive amounts of crops, but also create slick spots on the road as cars crush them. "They build up slowly over several years until you get a widespread outbreak," Sword says. The last big outbreak peaked around 2005, and the crickets are, for now, in decline in the West.

The Mormon cricket is actually a katydid rather than a true cricket. Hordes of them march across the landscape in long columns, devouring all the crops they come across. They will eat almost anything that gets in their way—including their fellow crickets. In fact, cannibalism is the reason for the march: One Mormon cricket will try to eat the cricket in front of it and simultaneously avoid becoming lunch for the cricket behind it, causing the entire column to move forward. "It's a forced march driven by cannibalism," Sword says.